Enallagma vernale
| Enallagma vernale | ||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Systematics | ||||||||||||
|
||||||||||||
| Scientific name | ||||||||||||
| Enallagma vernale | ||||||||||||
| Gloyd , 1943 |
Enallagma vernale is a species of dragonfly from the family of the slender dragonflies (Coenagrionidae), which is distributed in the extreme northeast of North America and southeastern Canada. Moor lakes, ponds and slow flowing rivers are settled. Enallagma vernale is a typical representative of the numerous group of blue-colored cup maids and is confusingly similar to the other members, especially the Enallagma annexum and Enallagma boreale, which are almost identical in ecological requirements.
features
Enallagma vernale is a typical slender dragonfly with a body length of 30 to 34 millimeters and a length of the rear wing of 18 to 20 millimeters. The males have a light blue basic color with large teardrop-shaped and also blue postocular spots on the body-facing side of the compound eyes . These are aligned with one another with the tip and connected to one another via a line. The eyes are dark on top, so that they appear to be covered by a cap. The median strip placed on the upper side of the front body ( thorax ) is noticeably wide, the lateral humeral strips are narrow. On the underlying light blue thorax sides there are two thorax lateral stripes, the upper one is only very rudimentary or not at all, so that the thorax side surface appears as if it were not drawn. The elongated abdomen is provided with a typical slender vial mark. The lower end of the second segment has a broad black horizontal line, often curved in the shape of a crescent. On the other segments three to seven there are caudally located, wider black rings, so that segments six and seven appear almost entirely black. The eighth and ninth abdominal segments are all blue, the tenth black on top again.
The abdomen of the females is more strongly built than that of the males and the upper side is predominantly dark in color, the abdominal segments only show a light ring at the front edge of segments three to eight. In front of the ovary, on the eighth abdominal segment, there is a protruding thorn. The light basic color of the dragonfly is most pronounced on segment eight, but there are also specimens with a completely blackened segment. Segments nine and ten are black. The eyes of the females are divided horizontally in color, the upper part is dark, the lower light brown, on the lower light part there is usually a dark horizontal stripe. The chest drawing corresponds to that of the male. As is not uncommon in the subfamily of the Ischnurinae , the females come in different color variants. There is an androchromic form, colored like the males, and a brown, heterochromic form.
Similar species
A relatively recent evolutionary split has led to a large number of species, some of which are very similar and difficult to distinguish, in North America. However, the cup youngsters are often formed from only one species, and once determined, it can be assumed that all specimens of this population only belong to this species. Preferences for different habitat types, which at first glance appear very similar, seem to separate them, even if these mechanisms are not yet fully understood.
Enallagma vernale cannot be distinguished from Enallagma annexum and Enallagma boreale without a detailed examination of the male abdominal appendages, which differ only in fine details . In E. vernale , each cercus has a button-like thickening at its distal end, at the foot of which there is a small black tooth next to a small depression. E. annexum lacks these characteristics, but intermediate types that share characteristics of both species appear again and again , either through natural variation or through hybridization . E. vernale is found relatively often in waters with fish stock, E. annexum seems to avoid them, or cannot reproduce here. Also very similar in the drawing of the thorax and abdomen are Enallagma civile , Enallagma ebrium and Enallagma hageni . The females of Enallagma vernale are also indistinguishable from the females of this species, even if the completely black eighth abdominal segment, which sometimes occurs in E. vernale , almost never occurs in these.
distribution
The distribution of Enallagma vernale extends from southwestern Ontario to Nova Scotia .
Way of life
Enallagma vernale inhabits bog lakes, ponds and slow flowing rivers. In contrast to Enallagma annexum , waters rich in fish are also accepted. In areas where the distribution overlaps with that of Enallagma annexum and Enallagma boreale , these are mostly found on bog lakes without fish. The males are - typical for the cup maid - to be found in large numbers near the water, where they fly low over the open water in large numbers or rest on the edge of dense vegetation structures. The mating usually takes place in sunny clearings near the water. The eggs are laid in floating vegetation that does not protrude from the water. Many possible egg-laying places are checked beforehand. The eggs are usually laid in tandem, the couple may separate and the female dives upside down to continue underwater. The male mostly guards his partner above the water surface, but often gives up after a while. There is hybridization with enallagma annexum .
The flight time begins in May and extends in the south of the distribution area into June, in the north partially into September.
swell
literature
- Dennis Paulson: Dragonflies and Damselflies of the East, Princeton Field Guides , Princeton University Press, New Jersey 2011, ISBN 978-0-691-12283-0 .
Individual evidence
- ↑ a b c d e f g Dennis Paulson: Vernal Bluet. In Dragonflies and Damselflies of the East , pp. 97-98.
- ^ Jill Silsby: Subfamily Ischnurinae (Blue-tailed Damselflies). In Dragonflies of the World . Smithsonian, Washington 2001, ISBN 1-560-98959-9 , pp. 110-112.
- ^ A b Dennis Paulson: American Bluets. In Dragonflies and Damselflies of the East , p. 85.
- ^ Dennis Paulson: Northern Bluet. In Dragonflies and Damselflies of the East , pp. 95-97.